You're making an assumption that there are no decent "designers" (what-ever that might be) that are not willing or able to utilize the Internet in the same way that FLOSS developers have.
I believe that there is evidence to the contrary. Consider the Appeal project for KDE (http://appeal.kde.org/wiki/Appeal), an Internet-enabled effort to make KDE 4.0 beautiful and, well, appealing.
I presume that it was this kind of "design" that you are speaking of because there is plenty of examples of good software design (as well as bad software design) in FLOSS projects.
But, in the end the "design" you are speaking of is a "matter of taste" issue. For instance: I find the Mac OS X stuff to be visually very nice (but I tire very much with the "brushed steel" look) but at the same time I find them to all have frustrating and annoying quirks and limitations.